Comparator



June 29 1926. 1,590,420

| w. CHUBB COMPARATOR Filed Jan. 14. 1921 wnuzsszs; INVENTOR Lew/5 14/. [kl/lb llllllllllf f Magi u Patented June 29, 1926.

UNITED STATES Lawns w. cnunn, or nncawoon rm, PENNSYLVANIA, ASSIGNOB 'ro wns'rmm PATENT. OFFICE.

HQUSEELEGTRIC & MANUFACTURING COMPANY, A CORPORATION 01' PENNSYL- VAN IA.

COMPARATOR.

Application fled January 14 19521. Serial No. want.

This invention relates to comparators and has special relation to devices of the aboveindicated character for use with alternating currents. a

One object of my invention is to provide an apparatus which shall be reliable and eificient in use.

Another object of my invention is to rovide an apparatus which shall be operable to either detect the presence of electrical disturbances or, specifically, to measure the values of alternating currents.

A further object of my invention is to adapt the herein described device to compare alternating currents with direct currents of to compare two or more independent alternating currents and to be able to determine the respective values in either instance.

Other and more specific objects of my invention will be apparent from the following description and claims.

My invention may be best understood by reference to the accompanying drawing, wherein- Figure 1 is a diagrammatic illustration of circuits and apparatus of one embodiment of my invention, and

Fig. 2 is a similar diagrammatic illustration of a modification of the apparatus of Fig. 1.

riefly, my invention may be stated to reside in the employment of a so-called string galvanometer with a Wheatstone bridge having two arms thereof of equal resistance and a third arm which is variable, these arms being of known value, and a fourth arm which is adapted to be varied in accordance with "applied currents, the whole bridge being supplied with a constant volta e.

The bridge is so arranged as to normall have at least two points of equal potentia connected between which 'is the galvanometer. However, if alternating current is ap-.

plied to one arm of the bridge, it will become unbalanced, with the result that a current will flow through the galvanometer. The potential across the galvanometer may again be adjusted to zero by means of the variable resistor which constitutes one arm of the resistance bridge.

Referring to Fig. 1, a bridge 1, having arms 2, 3, 4 and 5, is shown having constant voltage supplied thereto from a battery 6.

Obviously, the battery 6 is a conventional ment may be used therein which is readily sensitive to additional current. However, incandescent lamps, being readily responsive to the heat of an additional current to thereby vary their' resistance values, are preferable by reason of the fact that the herein described comparator is designed, for use with feeble currents. v

Iii this illustration, the arms of the bridge are shown as normally balanced, thereby producing equal potentials at the points 9 and 11 ofthe bridge. Connected between the points 9 and 11 is, preferably, a string galvanometer 12, through which no current ows when .the bridge is balanced.

An alternating-current circuit, designed to include the arm 5 of the bridge, also includes two condensers 13 and 14, which are connected in parallel to the arm 5. Alternatin current may be supplied to this circuit (not shown), through conductors 15, one of which is connected to a pointbetween the condensers 13 and 14 and the other of which is connected to a point between the lamps 7 and 8.

By reason of the insertion of the condensers in parallel to the resistor arm 5 and including them in the alternating-current circuit, alternating current will flow through the condensers and traverse the designated circuit, but no direct current can circulate past the condensers. Accordingly, there will be no intermingling of the currents, and, likewise, the value of this arm of the bridge will not be varied because of an additional path for the direct current.

Hence, when alternating current is impressed upon the circuit which includes arm 5 of the resistor, it will raise the temperature of the filaments of the lamps 7 and 8', thereby increasing their resistance to correspondingly unbalance the bridge. This action will change the potential value between points 9 and 11, thereby permitting current to flow throu h the g alvanometer 'to-indicate that the bridge is unbalanced. "If, now, it is desired to measure the value I of the alternating current from the circuit principle "of the invention described with 15, this may be accomplished by adjustin the variable resistor of arm 4 to effect equa potentials between the points-9 and 11.

Inasmuch as the value of the variable resistor is known, it will be apparent that, by the application of Ohmls law, the value of the alternating current may be determined in accordance with the amount of variance of the resistor. Or, in other words, the resistor 4 may be calibrated to'indicate the value of the alternating current by the corresponding position of its movable contact member when the galvanometer indicates a balance.

Referring toFig. 2, a modification of the 24 and 25, receiving current from a battery 26. The arms 23 and 24 are illustrated as including variable resistors, the values of which are known, and arms 22 and 25 are illustrated as including incandescent lamps 27 and 28, respectively. It will be noted that, in the foregoin description, the resistance value of these. amps has been referred to as increasing when current has been aplied thereto, which action will be true if amps of the tungsten type are used, which is preferable. However, if carbon lamps are used, the application of alternating current will cause a decrease'in the resistance value of the lam s. v

As descrilied with reference to Fig. 1, the bridge is constructed with at least two points 29 and 31, across which the potential value is normally equal. Between these points is connected a-string al'vanometer 32.

Arin 22 of the bri ge is adapted to be included in an alternating-current circuit which also includes the condensers 33 connected in parallel with the arm 22. The arm 22 is directly connected to a source of alternating current (not shown), leading from one of the conductors 34. The other conductor 34-is j adapted to be connected between the condensers.

In accordance with the foregoing description, if alternating current is applied to this circuit, the resistance value of the lamps 27 will be varied to thereby unbalance the bridge and permit current to flow throu h the galvanometer 32. The action will e similar to that described. for Fi 1, and the same measurements may be ma e in a manner similar to that described for Fig. 1,. by varying the value of the resistor of the arm 23 or that of the resistor of the arm 24,.

The arm 25 of the bridge .21 is likewise adapted to .be included in an alternatingcurrent circuit, which also includes the condensers 35, that are connected in parallel with the arm 25. This circuit is adapted to receive current from a'souroe of power (not shown),through supply conductors 36, one of which is directly connected to the arm 25, and the other of which is connected between the condensers 35. This source of power may be entirely independent from the source of power that is connected to the condensers 33. The independent-measurement of alternating currents applied to this arm of the resistor 'may be made as herei before described with reference to Fig. 1, by varying the value of the resistor arm 24 or that of the arm 23.

Assuming now that alternating current is simultaneously applied to the arms 22 and 25, thereby varying the resistance of both these arms. It will be apparent that these currents may be compared with each other, or the value of each may be determined, by the adjustment of the resistor arms 23 and 24.

An instrument of the above-indicated character has been found very desirable for detecting, comparing or measuring small alternating currents, as the alternating currents produce no potential difference across the galvanometer terminals, when connected in the manner illustrated.

It will be apparent that, in place of the galvanometer 12, a direct-reading indicator or measuring instrument could be connected across the bridge at the points of equal potentials so that the amount of deviation of this instrument would then be an indication of the value -of the alternating current applied to the arm 5. In this instance, equal potential could be restored across the terminals of the instrument, after the bridge has been unbalanced, by variation of the resistor 16 to restore the ratio of the arms of the bridge.

I do not wish to be restricted to, the specific circuit connections or arrangements of parts herein set forth, as various modifications thereof may be effected without departing from the spirit and scope of my invention. I desire, therefore, that only such limitations shall be imposed as are indicated in the appended claims.

I claim as my invention 1. In combination a Wheatstone bridge having one arm constituting a heater, direct-current means for energizing the bridge, and means for unbalancing the bridge in accordance with the current in an alternatingcurreut circuit comprising one conductor of said circuit connected to said arm at an intermediate portion thereof, another conductor of said circuit divided into two branches connected tofsaid arm adjacent to the ends thereof, and means in each of said branches for preventing the imposition of the direct current on said circuit.

2. In combination, a Wheatstone bridge, two heater elements connected in series relation in one arm of the bridge, direct-current means for energizing the bridge, and means for unbalancing the bridge in accordance with the current in an alternating-current circuit comprising one conductor of said circuit connected to said arm between said elements, another conductor of said circuit divided into two branches connected to said arm outside said elements, and means in each of said branches for preventing the imposition of the direct current on said circuit.

3. In combination, a Wheatstone bridge 'having one arm constituting a heater, directcurrent means for energizing the bridge, and means for unbalancing the bridge in accordance with the current in an alternating-current circuit comprising one conductor of said circuit connected to said arm at an intermediate portion thereof, another conductor of said circuit divided into two branches connected to said arm adjacent to the ends thereof, and a condenser in each of said branches.

4. In combination, a Wheatstone brid e, two heater elements connected in series re ation in one arm of the bridge, direct-current means for energizing the bridge, and means for unbalancing the bridge in accordance with the current in an alternating-current circuit comprising one conductor of said circuit connected to said arm between said elements, another conductor of said circuit divided into two branches connected to said arm outside said elements, and a condenser in each of said branches.

In testimony whereof, I have hereunto subscribed my name this 27th day of December, 1920. v

LEWIS W. CHUBB. 

